1. Field of the Invention
This invention pertains to the production of a compound safety pane comprising a sheet of glass and at least one layer of plastic material presenting energy-absorbent properties.
2. Background of the Prior Art
Compound safety panes containing a sheet of glass and at least one layer of plastic material have already been described in numerous publications.
Thus, French patent publication No. 2 398 606 (=UK 1 576 394) describes a compound pane containing a glass sheet, a layer of plastic material having energy-absorbent properties, formed from a thermoplastic polyurethane made from at least one aliphatic diisocyanate and at least one polyesterdiol or polyetherdiol, with the ratio of equivalent NCO groups to equivalent OH groups being preferably between 0.8 and 0.9, and a layer of plastic material having surface properties, especially good resistance to scratching and abrasion. This pane maintains its good optical properties and adhesion between the elements remains good under highly variable conditions of temperature and humidity, but the biomechanical properties of the pane and especially the resistance to shock are not entirely satisfactory.
Moreover, through European patent publication No. 0 054 491, a compound pane having the structure described above is known and for which the inserted layer of plastic material having energy-absorbent properties has a polyurethane-polyurate base, presenting a linear structure and a carbamide group content of about 1 to 20% by weight, with this polyurethane-polyurate being the reactive product of a prepolymer coming from a polyalcohol compound and an isocyanate compound taken in excess, with at least one diamine. This inserted layer is produced by the extrusion of a polyurethane-polyurate resin or by pouring a solution of said resin and evaporating the solvents, which, in both cases, requires several successive operations.
In the case of the extrusion, it is necessary to conduct a prior synthesis of the resin so that it can be extruded.
Moreover, to obtain the necessary optical quality for the intended application, the sheet must be "pressed". This optical quality obtained, moreover, does not generally last over time, because the plastic material retains its production process in memory and the quality produced by the "pressing" is reduced over time.
In addition, the extrusion of the layer having the energy-absorbent properties presents a problem of assembly with the self-repairing layer.
In the case in which the solution is poured, it is also necessary to conduct a prior synthesis of the resin. Next, the resin must be dissolved in a solvent, then the solution must be poured and the solvent must be evaporated in a repetitive manner to obtain a layer whose thickness is compatible with the desired energy-absorbent nature. The evaporation of the solvent also constitutes a source of harmful effects.
The invention obviates the drawbacks which have been mentioned and proposes a process for the production of a safety pane utilized especially as a vehicle windshield, which presents good optical and bio-mechanical properties and which maintains said properties under variable conditions of temperature and humidity.